1. Field of the Invention
The present invention relates to a portable inverter power generation apparatus that converts AC electric power into DC electric power, converts the DC electric power obtained by the conversion into AC electric power, and outputs the AC electric power to an exterior.
2. Description of the Background Art
Power supplies for electric tools or lighting fittings used outdoors such as building sites, construction sites, or street stalls include portable inverter power generation apparatuses. In the portable inverter power generation apparatus, a rectifying circuit rectifies AC electric power generated from an electric generator by the rotation of an engine to convert the AC electric power into DC electric power, and an inverter circuit converts the DC electric power obtained by the conversion into AC electric power and outputs the AC electric power to the exterior.
In this portable inverter power generation apparatus, the rotational speed of the engine is increased when a load current increases, while being decreased when the load current decreases. The load current corresponds to an AC output current of the electric generator.
JP 2003-284397 A and JP 2006-217780 A, for example, discuss detecting, in an inverter power generation apparatus, an AC output current output from an inverter circuit to the exterior using a current sensor, to determine a target rotational speed of an engine based on the detected AC output current and to control the rotational speed of the engine to be the determined target rotational speed. Thus, the rotational speed of the engine can be controlled so that a suitable current can be supplied to a load according to the state of the load.
On the other hand, JP 11-103501 A discusses a control device for an electric generator used in a hybrid vehicle. A method and an operation for controlling the electric generator used in the hybrid vehicle respectively differ from a method and an operation for controlling the portable inverter power generation apparatus. In the control device discussed in JP 11-103501A, required generated electric power of the electric generator is operated based on traveling conditions of the vehicle and an amount of charge of a battery. The rotational speed of an engine for driving the electric generator required to generate the required generated electric power (required rotational speed) is acquired from map data, and the rotational speed of the engine is set based on the required rotational speed. When the required rotational speed is within a resonance region between the engine and the electric generator, the rotational speed of the engine is set outside the resonance region. This results in prevention of noise caused by resonance between the engine for driving the electric generator and the electric generator.
In the electric generator used in the hybrid vehicle, the control device not only sets the target rotational speed of the engine in response to an AC output current of the electric generator but controls the rotational speed of the engine based on the traveling conditions of the vehicle and the amount of charge of the battery. The rotational speed of a multiple cylinder engine used in the hybrid vehicle smoothly changes. Therefore, the AC output current of the electric generator hardly severely increases and decreases in a short period of time.
On the other hand, the AC output current of the portable inverter power generation apparatus may severely increase and decrease in a short period of time depending on the state of a load. Since no battery is generally provided in the portable inverter power generation apparatus, a change in a load current is not mitigated by charging and discharging the battery. When a controlling method similar to that for the electric generator used in the hybrid vehicle is applied to the portable inverter power generation apparatus for setting the rotational speed of the engine based on the AC output current of the electric generator, therefore, a great burden may be imposed on the engine. In the portable inverter power generation apparatus, therefore, it is desired that the resonance of the engine is suppressed without imposing the great burden on the engine.